One of the things I was looking for before I bought my WRX was a straight up comparison between the RSX I had been driving and the WRX. While I didnt find it, I did find some good info. That being said, I thought I would share my thoughts between the two cars.
RSX; 2005 RSX-S, all stock except for motor mounts, Injen CAI w/bpi velocity stack/K&N filter. 53k miles, powdercoated stock 17's. (14.8 @ 98mph w/street tires)
WRX; 2005 WRX, bone stock. 70k miles.
First things first..
Launch - I think we all know, that it wasnt even a contest. Compared to the RSX, with its jerky, torque steering, wheel hopping start, the WRX was like heaven. The WRX just loves to go from a dead stop, and even in the rain, seemed to be glued to the road.
Speed - I feel like the WRX stock is only a little bit faster than the RSX. Overall, the WRX is alot smoother on power delivery, and has less seat of the pants pull, but I can tell I am getting up and going faster. One thing that the RSX has over the stock WRX is the sharp increase in power delivery, which gives you a 'kick in the pants' feel and once you are in that VTEC zone, you dont drop out of it even when you shift, so this feeling presists as you go through the gears. This to me FEELS funner, even though I know the WRX will be much better than the RSX when its modded a little bit.
Trans - Really the only part of driving the WRX I was not impressed with. While it is acceptable, compared to the RSX gearbox it leaves alot to be desired. The Acura shifts like butter and of course, has the 6 speed trans, while the WRX seems to be more abrupt in going into gear, and the act of shifting takes a longer throw and feels more visceral in the linkage. I do understand that the STi has a 6 speed, so I am only giving my opinion on the WRX 5 speed gearbox.
Handling/ride - While the RSX has good handling, it really wasnt even close to the WRX as far as stability, 'control' feel, and loss of traction. And though I have seen alot of complaints about the ride of the WRX I have to say that it seems to be softer and nicer than the very stiff suspension that the RSX has. As I mentioned above, the WRX stuck like glue even in the rain. The RSX, along with traction/wheelspin problems, even with good street tires I could get them to protest under a much lighter load than what I was able to do with the WRX.
Fit and Finish - I know being an Acura the RSX is 'supposed' to be nicer and really, it is. The interior is just better quality in RSX. The BOSE sound system is much better in the RSX. One thing I will miss about the RSX is the leather, while it wasnt the best leather ever, for me, leather > cloth any day. A bonus for the WRX though, is that even with cloth, I got heated seats, which you could only get in a Canadian RSX. Big plus for me as I live in an area with cold winters. While the WRX isnt as 'nice' as the Acura its not bad. The only thing in the WRX that actually feels cheap to me is the headlight/cruise control/wiper switches. Overall the cloth interior (perfect shape in this car) seems to have a good fit and finish and feels good, as does the rest of the interior and extrior trim. Both vehicles seemed to have about the same amount of road noise.
Looks - Its really a tie. I love the way my RSX looks, but the WRX is great looking in its own right. Both cars are compact, with the RSX being very angular and having great lines. The WRX looks more aggressive due to the hood scoop and wing, but needs a little more offset to look really really great.
Other - If you cannot tell, I did trade for the WRX. I work at a car dealership and we took the car in on trade, and the modder in me was instantly locked on. The WRX did have 20k more miles, but I am getting money back my way for my RSX. Also, I can do alot more with the WRX for alot less money. That K20 motor in the RSX is just so expensive too mod enough to make fast. I can probabaly get double, or even more, 'dollar to 1/4 mile tenths' increase for my money in the WRX.
Hope that helps anyone with the same dilemma!